Inorganic membrane is a type of membrane manufactured by inorganic material. Although the inorganic membrane appeared later than organic membrane, it developed rapidly with bright prospect. Inorganic membrane was researched and applied in 1840s for the first time, and then the technology of ultrafiltration and microfiltration of inorganic membrane was established and developed from 1980s to 1990s. During the development, large amount of the inorganic membrane products were invented and applied in industry, and replaced some organic polymer membranes in the industry field of water treatment, dairy products and beverages, etc. In 1980s, a breakthrough was occurred in the preparation technology of inorganic membrane. Burggraf et al from Twente University prepared microporous ceramic membrane with multi-layers and asymmetric structure through Sol-Gel technology, and the diameter of pore could be less than 3 nm. This type of membrane was even capable of separating gas, thereby became a strong competitor of organic polymer membrane. The Sol-Gel technology brought the research of inorganic membrane, especially the ceramic membrane, into a new stage. In 1990s, the research and application of inorganic membrane were developed to the 3rd phase, that is, focusing on application of gas separation and, another one, using ceramic membrane as both separator and reactor, and primarily on the former one.
Ceramic membrane is a type of inorganic membrane most widely used recently. Comparing with organic membrane, the advantages of ceramic membrane are as following: 1) having good thermal stability, and suitable for high-temperature and high-pressure system, the operating temperature is up to 400° C., even up to 800° C. sometimes; 2) having good chemical stability, acid-resistant, alkalescence-resistant, and the wide range of pH adapted for use; 3) having good antimicrobial properties, and absence of reaction with common microorganism; 4) having high mechanical strength of inorganic membrane assembly; Inorganic membrane is usually used in the form of carrier membrane, and the carriers are microporous ceramic material and porous glass, etc., prepared through high pressure and roast, the carriers would be roasted at high temperature again after the membrane is coated, which makes the membrane very solid without easy drop and rupture; 5) the membrane itself is nontoxic, and it would not contaminate the separation system, the membrane is also easy to renew and clean; When the membrane is blocked, back flushing, washing or cleaning chemically at high temperature could be used; 6) the pore diameter of the ceramic membrane has a narrow distribution to achieve high separation accuracy.
Halloysite Nanotubes (HNTs) are a kind of silicate inorganic material with natural nanotube structure, having excellent thermal and mechanical properties, and have bright application prospect in the field of reinforced or toughened polymer material, carriers for orientation drug release, etc. Existing preparation technology of ceramic membrane could not readily control the porosity and pore diameter of ceramic membrane quantitatively. Therefore, a ceramic membrane formed by membrane material in the form of HNTs, prepared through electronspinning technology, is required.